The present invention relates in general to elastic articulations also known as resilient joints. It is applicable notably, but not exclusively, to a vehicle suspension, in particular to a suspension for an axle of the type comprising two suspension arms, one end of which supports an axle arm receiving a wheel and the other end of which is integral with a shaft that is mounted in articulated fashion on the vehicle body through the intermediary of a resilient joint capable of operating in torsion and in compression/traction at the same time to provide the functions of spring suspension and filtration of vibrations or shocks.
The present invention relates in particular to a resilient joint with variable radial rigidity, the radial rigidity of which has a minimal value along a first reference axis of a system with three reference axes, the second reference axis of which merges with the axis of rotation of the resilient joint. Here xe2x80x9cradial rigidityxe2x80x9d means the rigidity of the joint in any direction perpendicular to the axis of rotation of the joint. Usually, in the case of a resilient joint for vehicle suspension, the above-mentioned xe2x80x9cfirst reference axisxe2x80x9d is oriented perpendicular or approximately perpendicular to a horizontal plane of reference linked to the vehicle body. Here xe2x80x9chorizontal plane of reference linked to the bodyxe2x80x9d means a plane that shifts parallel to the ground during travel of the vehicle under normal conditions.
Resilient joints with variable radial rigidity are already well known, notably through applicant""s European Patent EP 0,956,984. The resilient joint described in the said document comprises a cylindrical inner reinforcement, an outer reinforcement surrounding the inner reinforcement concentrically, and a sleeve made of elastomeric material, which is arranged between the inner and outer reinforcements and the inner and outer peripheral surfaces of which are linked without any possibility of sliding to the said inner and outer reinforcements. The elastomeric sleeve has at least one cavity, preferably two diametrically opposite cavities, which are positioned in such a way that the joint presents minimal radial rigidity along the above-mentioned first reference axis. Each cavity opens into at least one of the end surfaces of the sleeve, preferably into its two end surfaces, that is, in the first case, each cavity traverses the sleeve from one side to the other in a direction parallel to the axis of the joint. Each cavity additionally has a curved shape in the circumferential direction of the sleeve. The fatigue resistance of such a known resilient joint is hard to guarantee under all conditions of use.
In addition, with the resilient joint described in European Patent EP 0,956,984, it is relatively difficult to refine the direction in which the joint presents its minimal radial rigidity, in particular when the elastomeric sleeve operates in torsion, as is the case in a resilient joint with a suspension spring function. This difficulty may be thought to be due to the deformation in torsion of the elastomeric sleeve, which deformation modifies the geometry of the sleeve when the resilient joint bears the rated load for which it is designed.
Therefore, the object of the present invention is to furnish a resilient joint with variable radial rigidity, capable of operating in compression/traction and in torsion, and presenting improved fatigue resistance under compression/traction stresses as well as under torsional stresses.
The object of the present invention likewise is to furnish a resilient joint with variable radial rigidity, of which the direction in which radial rigidity is minimal may be greatly refined.
The present invention furnishes a resilient joint with variable radial rigidity designed to be mounted so as to operate in compression/traction and in torsion at the same time, in particular for a vehicle suspension, comprising an inner reinforcement, an outer reinforcement surrounding the inner reinforcement, and a sleeve made of elastomeric material, which is arranged between the inner and outer reinforcements and the inner and outer peripheral surfaces of which are linked without any possibility of sliding to the said inner and outer reinforcements, the said sleeve being configured such that the joint has a minimal radial rigidity along a first reference axis of a system with three reference axes, whose second reference axis merges with the axis of rotation of the resilient joint, characterized in that at least one of the two end surfaces of the sleeve has a profile that moves continuously in the circumferential direction of the sleeve between at least a minimum and at least a maximum, and in that the profile, in the inner peripheral zone of the said end surface, has at least a minimum and at least a maximum which are offset by a predefined angle respectively relative to at least a minimum and at least a maximum of the profile in the outer peripheral zone of the said end surface when no load is applied to the joint.
The said predefined angle preferably is selected in such a way that, when the joint is subjected to a reference load producing relative rotation of the said predefined angle of the inner and outer reinforcements relative to one another, the geometric loci of the minima and the geometric loci of the maximums of the profile between the said inner and outer peripheral zones are oriented approximately radially respectively along the first reference axis and along the third reference axis of the system with three reference axes.
Preferably, in each of the said inner and outer peripheral zones and in the intermediate zones, the said profile has two minima and two maximums along the circumference of the sleeve made of elastomeric material.
Preferably, the two end surfaces of the sleeve have a wavy profile. The wavy profile has for example an approximately sinusoidal or pseudo-sinusoidal shape.
Preferably, the first reference axis is approximately perpendicular to a horizontal plane linked to the vehicle body.
In one embodiment of the invention, the outer reinforcement is made up of a cylindrical collar or sleeve that is fixed rigidly in a predefined angular position in a bore of a supporting piece designed to be fixed to the vehicle body.
The supporting piece may be made up of a side rail, which has at least one supporting surface, preferably two supporting surfaces, capable of cooperating with at least one corresponding supporting surface on the vehicle body, so that, after fixation of the rail to the said body, the three reference axes of the resilient joint have predefined orientations relative to a system of reference axes linked to the vehicle body.